In photographic processing, the unexposed silver halide is usually complexed with alkali or ammonium thiosulfates after development and more or less thoroughly removed by subsequent washing. The completeness with which the silver thiosulfate complexes are removed is determined by the duration and temperature of this treatment step and by the support used for the photographic layer, for example baryta paper, polyethylene-laminated paper or cellulose acetate, polyester or the like for film. On average, it takes at least 30 minutes' washing at approximately 25.degree. C., although thiosulfates can still remain behind. In this case, patchiness can occur during the storage of the silver images, because the image gradually changes hue either completely or locally from black to brown or yellow. This is attributable to the formation of silver sulfide formed by the decomposition of the residual thiosulfate.
A similar troublesome change in image hue occurs when photographic silver images are exposed to the effect of oxidizing gases. Oxidation of the image silver results in the formation of water-soluble silver salts which can diffuse in the material. The photolysis of these soluble silver salts results in the formation of finely divided yellow to red-brown colored colloidal silver or, alternatively, brown colored silver compounds are formed. These troublesome changes frequently occur in the final photographic silver image in the form of so-called microspot defects.
There has been no shortage of attempts to avoid or reduce these troublesome subsequent changes in the photographically produced silver images, for example by washing the chemicals required for the processing of the exposed photographic recording materials more thoroughly or by storing the processed recording materials, i.e. the final silver images, under standardized atmospheric conditions.
Various processes have been described with a view to reducing the washing time and avoiding the adverse effects of the thiosulfate impurities. One useful method of converting residual thiosulfate into photographically harmless compounds is to use monochlorine or monobromine compounds, such as for example chloroacetic acid in accordance with DE-A-1 522 428. In an aftertreatment bath which contains the monochlorine or monobromine compound mentioned above and which follows the shortened washing step, the thiosulfates are converted into the corresponding salt of a thiosulfuric acid S ester known as Bunte's salt.
These compounds are no longer able to react as thiosulfates with the image silver. However, it was not possible completely to dispense with the washing following the fixing step as long as baryta paper or other papers without a plastic coating were used as supports. By contrast, final washing can be dispensed with altogether if plastic-coated papers, such as for example polyethylene-coated paper or acetyl cellulose in the case of film, are used as support for the photographic layer.
In order to counteract harmful environmental influences in the form of oxidizing gases, various classes of compounds have already been proposed for stabilizing silver images, generally being used in additional finishing baths after the final washing bath.
The compounds in question include non-cyclic or cyclic thiosemicarbazides (DE-A-20 00 622), heterocyclic mercapto or thione compounds of the tetrahydropyrimidine, thiazine or tetrazine type (DE-A-20 13 423), organic and inorganic thiocyanates (DE-A-22 18 387) and isothioureas (U.S. Pat. No. 4,500,632). However, these compounds do not satisfy practical requirements because their stabilizing effect is inadequate or because the photographic properties of the layers are undesirably influenced.
Other processes are known in which stabilizing additives are directly incorporated in the photographic silver halide material. Thus, DE-A-31 51 182 (GB-A-2,090,991) describes the incorporation of polyvinyl imidazole while GB-A-1,156,167 describes the incorporation of sulfoalkyl-substituted hydroquinones.
However, relatively high concentrations of 0.5 g/m.sup.2 heave to be used in their case to obtain adequate stabilization. The compatibility of the polyvinyl imidazole itself with silver halide emulsions, with wetting agents, stabilizers, developers and auxiliary developers is extremely critical. In addition, high concentrations in the protective layer lead to a reduction in gloss.
A process for stabilizing photographically produced silver images which obviates the disadvantages mentioned above has now been found which eliminates the need for washing after fixing in the case of plastic-coated photographic paper and which uses a stabilizing bath containing both an aliphatic monochlorine compound or monobromine compound and an aminotetrazole or amino-1,2,4-triazole in certain quantities as stabilizing compounds.